Wound dressings have long been used in the art to protect and help heal wounds or skin eruption on areas of the body that have been injured. Generally, it is well known to combine an adhesive material with a plastic layer or film or with a foam layer or both. For instance, U.S. Pat. No. 4,743,499, owned by the assignee of record, is directed toward a hydrocolloid laminate which comprises a lower layer of hydrocolloid adhesive and an upper layer of flexible open-cell polymer foam. A first film layer is interposed between the adhesive layer and the foam layer while a second film layer is provided on the foam layer on the side opposite the first film layer.
With respect to adhesive compositions used for wound dressings, various compositions have long been known in the art. For example, Chen U.S. Pat. No. 3,339,546 discloses a blend of rubbery elastomer such as polyisobutylene and one or more water soluble or water swellable hydrocolloids such as a powdery mixture of pectin, gelatin, and carboxymethyl-cellulose. The adhesive mass has a water insoluble material applied to one surface. Such a dressing is commercially available from E. R. Squibb & Sons, Inc. under the trademark Stomadhesive and is used as a skin barrier around stomas to prevent skin breakdown by the corrosive fluids discharged by the stoma.
In hydrocolloid adhesive compositions of this type, the polyisobutylene is hydrophobic but provides the adhesive properties required of the dressing. The hydrocolloid powders are hydrophilic, and therefore, when the adhesive composition is placed in contact with an exuding wound, the water from the wound, upon penetrating the adhesive, is absorbed by the hydrocolloid particles.
However, a major problem with these: compositions is their susceptibility to breakdown and fragmentation upon exposure to the wound exudate and body fluids. Notably, the hydration of the hydrophilic hydrocolloid particles begins at the adhesive/wound interface and progressively hydrates deeper into the adhesive composition. The hydrocolloid particles typically hydrate to 20 or 30 times their weight in water, producing large domains of water or fluid suspended in the polymer phase. Thus, with time, due to the large difference in the surface tension between the polymer phase and the liquid phase, there is a phase reversal at that part of the adhesive near the adhesive/wound interface wherein the water or fluid phase becomes dominant and has small fragments or pieces of pure polymer therein.
At this point, the adhesive composition has disintegrated such that it no longer is a solid polymer adhesive, but rather, becomes a paste or gel on the surface of the wound. Hence, when the dressing is removed, a residue remains in the wound requiring removal, typically by irrigation or washing. Furthermore, when this phase reversal occurs, the dressings have been known to lift off the wound and allow leakage of exudate.
Several attempts have been made heretofore to improve the integrity of the hydrocolloid adhesive composition. For example, a mixture of low and high molecular weight polyisobutylenes, mixed so that both polymers are in a continuous phase, has been used as a wound dressing and is available from the assignee of record under the tradename Duoderm. Similar to the composition described in U.S. Pat. No. 3,339,546, this composition includes a blend of gelatin, pectin (citrus), and sodium carboxymethyl cellulose embedded in the matrix of the dressing at approximately 40 percent by weight. The ingredients are not in a continuous phase, but are powders in their particulate form.
U.S. Pat. Nos. 4,192,785 describes incorporating into the adhesive composition a cohesive strengthening agent such as natural or synthetic fibrous material, finely divided cellulose, cross-linked dextran, and cross-linked carboxymethylcellulose or a starch-acrylonitrile graft copolymer. The cohesive strengthening agent is reported to control the rate of hydration of the composition thereby increasing resistance to disintegration by body fluids.
U.S. Pat. No. 4,551,490 also discusses the use of cohesive strengthening agents to control the rate of hydration of the composition. Moreover, the patent indicates that styrene radial or block type copolymers such as styrene-butadiene-styrene (S-B-S) and styrene-isoprene-styrene (S-I-S) block type copolymers may be used as a component of the pressure., sensitive composition. These block type copolymers are available from Shell Chemical Co. under the tradename Kraton. No reason is given for their use.
A composition similar to the adhesive composition disclosed in U.S. Pat. No. 4,551,490 is available from the assignee of that patent, E. R. Squibb and Sons, Inc., under the tradename Control Gel Formula (CGF). This composition is a mixture of polyisobutylene, a thermoplastic polymer such as styrene-butadiene-styrene (S-B-S) block copolymer, and hydrophilic powders. The; S-B-S block copolymer is reported to create a thermodynamically stiff, three-dimensional matrix with embedded polyisobutylene and hydrophilic powders. This three-dimensional matrix is said to be resistant to phase reversal as described hereinabove because of its three-dimensional structure and the polarity of the S-B-S moiety.
U.S. Pat. No. 4,952,618 is directed toward a hydrocolloid adhesive composition comprising a rubbery elastomer having water soluble or water swellable hydrocolloid particles dispersed therein, at least a portion of which are polycationic hydrocolloid particles. The patent teaches that the compositions have an absorbency value of at least 180 percent and an integrity value of at least 60 percent.
Thus, none of the known art has heretofore provided an adhesive composition which maintains the integrity of the composition through the use of polyisobutylene and the addition of random copolymers of styrene and butadiene (SBR) or halobutyl rubber.